Not another soul was found in it whose name was not registered on the chart.

As I have already said, the guilty one had managed to escape immediately upon the flight of the arrow, though how, even then, he could have got below in the time he did is a mystery which trips me up every time I think of it.

But letting that go for the present, he did get there and get there unnoticed.

How?
Now, there are three ways of escape from behind either of those pedestals.

The way Travis took, that is, toward the front, and round through the suite of rooms headed by the one marked H, to the rear staircase; the more direct one of an immediate exit from the gallery through Sections VI and VII to this same staircase; and (the only one worth considering) a straight plunge for the door behind the tapestry and so down by the winding staircase beyond, into the Curator's office.